During the repairing process of a thin film transistor liquid crystal display (TFT-LCD) module, long pressing heads and short pressing heads are used to fix a substrate to be welded in a position. A welding machine typically has a plurality of pressing heads which are attached to a support. The pressing heads need to be replaced to meet the fabrication requirements of products having different sizes, and the plurality of pressing heads need to be horizontally calibrated to meet the requirements of production process and to guarantee the plurality of pressing heads have the same press level during the fabrication process. There is an independent fixing position for each of the plurality of pressing heads. Moreover, spaces between individual independent pressing heads are relatively large. The plurality of pressing heads are connected to each other through sliding rod, and the spaces may be increased according to the real production. However, the adjusting process for the plurality of pressing heads respectively is complicated and time consuming.